Calculating Keq
1. Write a balanced chemical equation with states
2. Write the equilibrium expression
3. Find the molar concentrations of all species at equilibrium
4. Sub the equilibrium concentrations into the expression and solve
For homogeneous gas phase equilibrium, you may use the partial pressure of gas to calculate the value of K.
The magnitude of Keq
- The magnitude of the equilibrium constant, Keq, indicates the extent to which the reaction proceeds or which side of the reaction is favoured
- If Keq>>>1, the reactions said to go to completion (i.e. at equilibrium the products are highly favoured)
- If Keq<<<1, the reaction proceeds only slightly (i.e. at equilibrium the reactants are highly favoured)
- If Keq=1, neither side is favoured (i.e. at equilibrium the [products] = [reactants]) Calculating equilibrium concentrations AKA ICE problem
- The equilibrium expression can be used to calculate the concentration of all species at equilibrium. Follow the steps below
1. Write a balanced chemical equation with states
2. Determine any initial concentrations in mol/L
3. Set up an ice table
4. Let x represent any changes in concentration. Multiply x by the molar ratio and indicate if it is an increase or decrease by the sign of the change (+ or -)
5. Write the Keq expression
6. Check if the approximation rule works
7. Solve for x
8. Answer the question Homework
sheets
Pg. 447 # 41-50
Tuesday, May 5, 2015 By Alex Prieditis
Le Chatelier's Principle
- When a stress is applied to a system at equilibrium, the equilibrium will shift (increase in speed) in the direction to relieve the stress
- A stress can be a change in concentration, volume, pressure, temperature,or an addition of an inert species
- Exothermic reactions have a negative delta H value
- Endothermic reactions have a positive delta H value
The Effects of Stresses on Equilibrium
Increase [C] = shift to use the material
Decrease [C] = shift to make material
Increase Volume/Decrease pressure = shift to side with more gas molecules
Decrease Volume/Increase pressure = shift to side with less gas molecules
Increase temperature = shift in endothermic direction
Decrease temperature = shift in exothermic direction
Add catalyst = nothing
Add solid = nothing
Add inert gas at constant volume = nothing
Add inert gas at constant pressure = volume increases therefore will shift to side with more gas molecules
Temperature is the only thing that can change Keq
Homework:
sheets
Representing Equilibrium Graphically
By: Ginushanth Suriyakumaran
-It is possible to determine the point at which equilibrium is reached by constructing a concentration vs time graph for a reversible reaction
-Since equilibrium is reached when there is no net change in the concentration in reactants and products, the slopes of all lines on the graph will be zero at equilibrium
-The y-axis of the graph is concentration and the x-axis is time
The equation for this made-up reaction is 2R(g) ⇌ 3 P(g) + energy, R meaning reactants and P, meaning products
This graph is an example of how equilibrium is represented graphically
At T1, there was an increase in reactants. This causes the reaction to shift right and as a result, the concentration of reactants gradually decreased while the concentration of products gradually increased. However, when there is a change in concentration, there will be a spike then a gradual decrease or increase just like at T1 for reactants
At T2, the volume of the system was decreased. When the volume decreases, the concentration of gas increases because the volume decreases. The concentration is represented by moles/litre and so if the litres is reduced, the number becomes larger. Not only that, if the volume decreases, the pressure inside the system increases. As a result, the reaction shifts left because as pressure increases, the reaction shifts toward the side with fewer gas particles. Similarly at T1, there is a spike upward for both reactants and products. This is because there was a change in concentration of both the reactants and products. Afterward, there is a gradual increase for the reactants and gradual decrease for the reactants.
At T3, there is a change in temperature as the overall temperature decreases. This causes the reaction to shift right because it wants to produce more heat. This causes a gradual increase products and gradual decrease in reactants
Not only that, you must also note that the concentration of the reactants and products is larger than its initial concentration prior to the change
A curve will spike upward or downward if the change in the system is a change in concentration of either the products or reactants or both.
In order to successfully draw the graph along with the changes that occur to each curve, you must understand Le Chatelier's principle because it will allow you to know whether or not the change affects the curve or how to change the curve based on the change in the system.
Homework: Do the equilibrium graphs on the back of one of the handouts.
Monday, May 4, 2015 By Alex Prieditis
Calculating Keq
1. Write a balanced chemical equation with states
2. Write the equilibrium expression
3. Find the molar concentrations of all species at equilibrium
4. Sub the equilibrium concentrations into the expression and solve
- For homogeneous gas phase equilibrium, you may use the partial pressure of gas to calculate the value of K.
The magnitude of Keq- The magnitude of the equilibrium constant, Keq, indicates the extent to which the reaction proceeds or which side of the reaction is favoured
- If Keq>>>1, the reactions said to go to completion (i.e. at equilibrium the products are highly favoured)
- If Keq<<<1, the reaction proceeds only slightly (i.e. at equilibrium the reactants are highly favoured)
- If Keq=1, neither side is favoured (i.e. at equilibrium the [products] = [reactants])
Calculating equilibrium concentrations AKA ICE problem
- The equilibrium expression can be used to calculate the concentration of all species at equilibrium. Follow the steps below
1. Write a balanced chemical equation with states
2. Determine any initial concentrations in mol/L
3. Set up an ice table
4. Let x represent any changes in concentration. Multiply x by the molar ratio and indicate if it is an increase or decrease by the sign of the change (+ or -)
5. Write the Keq expression
6. Check if the approximation rule works
7. Solve for x
8. Answer the question
Homework
sheets
Pg. 447 # 41-50
Tuesday, May 5, 2015 By Alex Prieditis
Le Chatelier's Principle
- When a stress is applied to a system at equilibrium, the equilibrium will shift (increase in speed) in the direction to relieve the stress
- A stress can be a change in concentration, volume, pressure, temperature,or an addition of an inert species
- Exothermic reactions have a negative delta H value
- Endothermic reactions have a positive delta H value
The Effects of Stresses on Equilibrium
Increase [C] = shift to use the material
Decrease [C] = shift to make material
Increase Volume/Decrease pressure = shift to side with more gas molecules
Decrease Volume/Increase pressure = shift to side with less gas molecules
Increase temperature = shift in endothermic direction
Decrease temperature = shift in exothermic direction
Add catalyst = nothing
Add solid = nothing
Add inert gas at constant volume = nothing
Add inert gas at constant pressure = volume increases therefore will shift to side with more gas molecules
Homework:
sheets
Representing Equilibrium Graphically
By: Ginushanth Suriyakumaran
-It is possible to determine the point at which equilibrium is reached by constructing a concentration vs time graph for a reversible reaction-Since equilibrium is reached when there is no net change in the concentration in reactants and products, the slopes of all lines on the graph will be zero at equilibrium
-The y-axis of the graph is concentration and the x-axis is time
The equation for this made-up reaction is 2R(g) ⇌ 3 P(g) + energy, R meaning reactants and P, meaning products
Homework: Do the equilibrium graphs on the back of one of the handouts.
Extra Resources: